This invention relates to automobile headliners, and more particularly to automobile headliners comprising a panel formed of a batt of polymeric fibers that is compressed and molded into a predetermined contoured shape that is resiliently flexible.
Vehicle headliners have been fabricated from a variety of thermoformable fibrous batts comprised of inorganic fibers such as glass, natural fibers such as flax, sisal or the like, synthetic polymer fibers, and combinations of these fibers.
In the case of vehicle headliners comprising a panel formed from a batt of inorganic and/or natural fibers, shape retention has been achieved by impregnating the fibrous batt with a thermosettable resin that cures when the batt is heated. The thermoformable resin impregnated batt is heated before being compressed in a mold and/or while it is in the mold. After the resin has cured, the batt becomes relatively rigid and brittle. Because of this rigidity and brittleness, vehicle headliners comprised of fibrous batts that retain their desired shape using cured resins are subject to damage during installation, and must generally be installed through either the windshield opening or the rear window opening.
A currently preferred vehicle headliner construction that overcomes problems associated with the rigidity and brittleness of vehicle headliners comprising a panel of fibrous batt that retains its shape by virtue of cured resins is described in U.S. Pat. No. 4,840,832. This headliner utilizes a panel formed from a compressed and molded batt of polymeric fibers that are thermally fused together at a multiplicity of locations to impart to the panel a self-supporting molded rigidity to allow the headliner to retain its shape in an installed condition in a vehicle, while rendering the panel highly deformable and resilient to allow it to be flexed during installation and thereafter recover resiliently to its original molded shape. These properties enable the headliner to be bent or flexed nearly double to facilitate installation in a vehicle.
Although vehicle headliners having a panel formed from a compressed and molded batt of polymeric fibers that are thermally fused together at a multiplicity of locations are less susceptible to damage during installation than headliners using thermosettable resin binders, the thermoplastic fiber batts can exhibit excessive loss of thickness upon heating, which can prevent complete filling of the headliner mold. When this occurs, the resulting headliner does not have the desired predetermined shape, and must be scraped. Accordingly, there is a need to modify the known processes for making vehicle headliners having a polymeric fiber batt in which the polymeric fibers are thermally fused together at a multiplicity of locations, such that batt thickness loss is reduced during heating of the batt. More specifically, there is a need for modifying the process so that the polymeric fiber batt exhibits improved loft retention during heating.
Another problem with conventional vehicle headliners comprising a panel formed of a compressed and molded thermoplastic polymeric fiber batt is that the headliner is prone to plastic deformation and is still susceptible to damage and/or deformation during robust handling. Accordingly, it would be desirable to provide headliners of this type having improved mechanical properties.
It has been discovered that improved loft retention of polymeric fiber batts during heating can be achieved by appropriate selection of heating parameters and/or selection of polymeric fibers.
In accordance with one aspect of the invention, it has been determined that vehicle headliners having a panel formed of a compressed and molded thermoplastic polymeric fiber batt exhibiting improved loft retention can be achieved by heating the batt, either prior to or during the molding operation, at a temperature that is from about 20xc2x0 C. below the melting temperature of the thermoplastic fibers to about 20xc2x0 C. above the melting temperature of the fibers for a time sufficient to activate adhesive characteristics of the thermoplastic fibers.
In accordance with another aspect of the invention excessive loss of batt thickness during thermal processing is achieved by using thermoplastic fibers having a denier that is about 15 or higher. Thermoplastic fibers having greater cross-sectional areas exhibit greater loft retention during heating due to the increased stiffness of such fibers.
In accordance with another aspect of the invention, greater loft retention during heating is achieved by use of thermoplastic fibers having any cross-sectional geometry that imparts greater stiffness than thermoplastic fibers having a solid circular cross-sectional geometry. Preferred fiber cross-sectional geometries include hollow cross-sectional geometries, cross-sectional shapes having a plurality of rounded projections or lobes, such a trilobal or quadralobal geometry, and polygonal geometries, such a triangular, quadrilateral, or pentagonal geometries.
In accordance with another aspect of this invention, improved mechanical properties are imparted to a vehicle headliner comprising a panel formed of a compressed and molded thermoplastic polymeric fiber batt made of sheath-core bicomponent fibers having a core formed of a relatively high melting polyethylene terephthalate (PET) polymer and a sheath comprising a PET copolymer having a much lower melting temperature and exhibiting thermoplastic adhesive and thermoformability properties when heated. The improved properties are achieved by control of sheath polyester (PET) crystallization during the manufacturing process. More specifically, it has been discovered that the degree of crystallinity of the sheath polymer can be increased by appropriate thermal treatment, and that by increasing the degree of crystallinity of the sheath polymer the mechanical properties of the headliner can be improved. The resulting headliner is less prone to plastic deformation and can be handled more robustly without damage or deformation.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.